Light strengthens circadian rhythm and sharpens memory in older adults
STUDY: Li W et al, Journal of Applied Gerontology 2026
STUDY TYPE: Randomized, placebo-controlled trial
FUNDING: National Institute on Aging
Background
As we age, the brain’s response to light and dark dampens, worsening sleep, and in turn cognitive decline. A tailored lighting device showed positive results in dementia, and this trial it in mild cognitive impairment.
The Protocol
This was not traditional light therapy, which uses a much stronger, 10,000 lux device. Here, patients sat near a bright (300-500 lux), warm-white lamp for an hour shortly after waking.
The Study
- 61 older adults with MCI and disturbed sleep, mean age 70, living at home.
- Randomized to a bright, circadian-effective tabletop or floor lamp or a dim placebo lamp, used for at least an hour within two hours of waking, for 24 weeks.
- Cognition (Alzheimer’s Disease Assessment Scale-Cognitive Subscale), sleep (actigraphy), mood, and quality of life were tracked through 12 weeks after the lights were removed.
Results
The memory portion of the Alzheimer’s Disease Assessment Scale-Cognitive Subscale improved more with active light than placebo (mean change -1.33 vs 0.59 points, p = 0.035). The total score on that scale also favored active light, dropping nearly 2 points versus almost no change with placebo, though this didn’t reach statistical significance.
Sleep also improved with morning light. The percent of the night spent asleep, percent awake, and minutes awake after falling asleep all changed in favor of active light (p = 0.042, 0.023, and 0.031).
Mood and the Montreal Cognitive Assessment didn’t differ between groups.
Limitations
Only 61 of a planned 120 patients enrolled, largely due to COVID-19 disruptions. Light exposure outside the assigned hours wasn’t controlled, and differences in bulb brightness may have partly broken the blind.
Practice Implications
- In dementia, traditional light therapy improved agitation, mood, cognition, and sleep in a few randomized trials.
- This study suggests benefits with mild cognitive impairment as well, even at a lower dose of light.
—Chris Aiken, MD
Director, Psych Partners
Editor in Chief, Carlat Psychiatry Report
